U.S. patent number 7,471,358 [Application Number 11/555,880] was granted by the patent office on 2008-12-30 for liquid crystal display device.
This patent grant is currently assigned to Toshiba Matsushita Display Technology Co., Ltd.. Invention is credited to Tetsuya Iizuka, Hiroyuki Kimura, Hiroshi Tabatake, Keiji Tago.
United States Patent |
7,471,358 |
Tago , et al. |
December 30, 2008 |
Liquid crystal display device
Abstract
In order to make a boundary inconspicuous, which is located
between an image area which displays an image by translucent pixels
and a dummy area which always displays a white color by reflection
pixels, a size ratio of transparent areas in color filters of the
reflection pixels with respect to reflection areas therein is made
larger than a size ratio of transparent areas in color filters of
the translucent pixels with respect to reflection areas therein. In
such a way, brightness of the display is balanced by adjusting
quantities of transmission light through the transparent areas of
the reflection pixels with respect to quantities of reflection
light generated unexpectedly on transmission areas of the
translucent pixels. Then, degrees of whiteness in the translucent
pixels and the reflection pixels are approximated to each
other.
Inventors: |
Tago; Keiji (Fukaya,
JP), Tabatake; Hiroshi (Fukaya, JP),
Kimura; Hiroyuki (Fukaya, JP), Iizuka; Tetsuya
(Saitama, JP) |
Assignee: |
Toshiba Matsushita Display
Technology Co., Ltd. (Tokyo, JP)
|
Family
ID: |
38110292 |
Appl.
No.: |
11/555,880 |
Filed: |
November 2, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070121039 A1 |
May 31, 2007 |
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Foreign Application Priority Data
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Nov 22, 2005 [JP] |
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2005-337722 |
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Current U.S.
Class: |
349/114; 349/113;
349/108; 349/106 |
Current CPC
Class: |
G02F
1/133555 (20130101); G02F 1/133514 (20130101); G02F
1/133371 (20130101); G02F 1/133388 (20210101); G02F
2201/52 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101) |
Field of
Search: |
;349/113-114,106-109 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
US. Appl. No. 11/938,531, filed Nov. 12, 2007, Tago. cited by
other.
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Primary Examiner: Choi; Jacob Y.
Assistant Examiner: Jankowski; Keith
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A liquid crystal display device, comprising: an image area in
which a plurality of transflective pixels having reflection areas
and transmission areas are arrayed; a reflection display area in
which a plurality of reflection pixels having only reflection areas
are arrayed, the reflection area being disposed on a periphery of
the image area; and color filters in which clear areas are provided
for each color in the respective reflection areas of the
transflective pixels and the reflection pixels, wherein, with
regard to color filters of at least the same one color, a size
ratio of the clear areas in the reflection pixels with respect to
the reflection areas therein is larger than a size ratio of the
clear areas in the transflective pixels with respect to the
reflection areas therein, a size of the reflection areas of the
reflection pixels is equal to a size of the reflection areas of the
transflective pixels, and a size of the clear areas provided in the
color filters of the reflection pixels is larger than a size of the
clear areas provided in the color filters of the transflective
pixels.
2. A liquid crystal display device, comprising: an image area in
which a plurality of transflective pixels having reflection areas
and transmission areas are arrayed; a reflection display area in
which a plurality of reflection pixels having only reflection areas
are arrayed, the reflection area being disposed on a periphery of
the image area; and color filters in which clear areas are provided
for each color in the respective reflection areas of the
transflective pixels and the reflection pixels, wherein, with
regard to color filters of at least the same one color, a size
ratio of the clear areas in the reflection pixels with respect to
the reflection areas therein is larger than a size ratio of the
clear areas in the transflective pixels with respect to the
reflection areas therein, the color filters are the three colors
being red, green, and blue, a size of the reflection areas of the
reflection pixels is larger than a size of the reflection areas of
the transflective pixels, in the blue color filter, the size ratio
of the clear areas provided in the reflection pixels with respect
to the reflection areas provided therein is larger than the size
ratio of the clear areas provided in the transflective pixels with
respect to the reflection areas provided therein, and in each of
the red and green color filters, the size ratio of the clear areas
provided in the reflection pixels with respect to the reflection
areas provided therein is smaller than the size ratio of the clear
areas provided in the transflective pixels with respect to the
reflection areas provided therein.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2005-337722 filed on Nov. 22,
2005; the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a translucent liquid crystal
display device which displays an image by both of a light
reflection mode and a light transmission mode.
2. Description of the Related Art
In general, in the field of a mobile information terminal such as a
cellular phone and a mobile music player, a liquid crystal display
device is used for displaying an image and a character. In
particular, a translucent liquid crystal display device that
displays an image by a light reflection mode and a light
transmission mode has high visibility both indoors and outdoors. As
the translucent liquid crystal display device, for example, the one
disclosed in Japanese Patent Laid-Open Publication No. 2002-303863
is known.
In a conventional liquid crystal display device, as shown in FIG.
1, a frame-like black mask 3 has been provided on a periphery of an
image area 1, and an area between the image area 1 and a cabinet of
the mobile information terminal has been black.
In recent years, as a color of the cabinet of the mobile
information terminal has been being diversified, it has been
required that the area between the image area 1 and the mobile
information terminal be displayed white to enhance an appearance
thereof.
In usual, on the peripheral area between the image area 1 and the
black mask 3, a dummy area that always performs white display is
provided. In the image area, translucent pixels that have
reflection areas and transmission areas are arrayed, where a color
image is displayed by the light reflection mode and the light
transmission mode. In the dummy area, reflection pixels that have
only reflection areas are arrayed, where the white color is
displayed by the light reflection mode.
However, structures in the pixels are different between the
translucent pixels of the image area and the reflection pixels of
the dummy area. In particular, while external light is reflected
only on the reflection areas in the reflection pixels, the external
light is reflected not only on the reflection areas but also on the
transmission areas actually to some extent in the translucent
pixels. Therefore, differences occur in reflectance and color tone
between the image area and the dummy area, causing a problem that,
in the case of performing the reflection display of the white
color, a boundary therebetween becomes conspicuous.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the differences
in reflectance ratio and color tone between the image area that
performs translucent display and the dummy area owing to the
structural difference between the pixels thereof, and to make the
boundary between the image area and the dummy area inconspicuous in
the case of performing the reflection display of the white
color.
A first feature of the invention is in that a liquid crystal
display device includes: an image area in which a plurality of
translucent pixels having reflection areas and transmission areas
are arrayed; a reflection display area in which a plurality of
reflection pixels having only reflection areas are arrayed, the
reflection area being disposed on a periphery of the image area;
and color filters in which transparent areas are provided for each
color in the respective reflection areas of the translucent pixels
and the reflection pixels, wherein, with regard to color filters of
at least the same one color, a size ratio of the transparent areas
in the reflection pixels with respect to the reflection areas
therein is larger than a size ratio of the transparent areas in the
translucent pixels with respect to the reflection areas
therein.
In this invention, in the color filters of at least the same one
color, the size ratio of the transparent areas in the reflection
pixels with respect to the reflection areas therein is larger than
a size ratio of the transparent areas in the translucent pixels
with respect to the reflection areas therein. In such a way,
brightness of the display is balanced by adjusting quantities of
transmission light through the transparent areas in the reflection
pixels with respect to quantities of reflection light generated
unexpectedly on the transmission areas in the translucent pixels.
Moreover, since degrees of whiteness in the translucent pixels and
the reflection pixels are approximated to each other, differences
in reflectance ratio and color tone between the image area and the
dummy area can be improved, and a boundary between both thereof can
be made inconspicuous.
A second feature of the invention is in that a size of the
reflection areas of the reflection pixels is equal to a size of the
reflection areas of the translucent pixels, and a size of the
transparent areas provided in the color filters of the reflection
pixels is larger than a size of the transparent areas provided in
the color filters of the translucent pixels.
In this invention, the size of the reflection areas of the
reflection pixels is equalized to the size of the reflection areas
of the translucent pixels, thus making it possible to easily adjust
the size ratios only by the sizes of the transparent areas of the
reflection pixels and the translucent pixels.
A third feature of the invention is in that the color filters have
the three colors being red, green, and blue, a size of the
reflection areas of the reflection pixels is larger than a size of
the reflection areas of the translucent pixels, in the blue color
filter, the size ratio of the transparent areas provided in the
reflection pixels with respect to the reflection areas provided
therein is larger than the size ratio of the transparent areas
provided in the translucent pixels with respect to the reflection
areas provided therein, and in each of the red and green color
filters, the size ratio of the transparent areas provided in the
reflection pixels with respect to the reflection areas provided
therein is smaller than the size ratio of the transparent areas
provided in the translucent pixels with respect to the reflection
areas provided therein.
In this invention, the size of the reflection areas of the
reflection pixels is larger than the size of the reflection areas
of the translucent pixels, and in the blue color filter, the size
ratio of the transparent areas provided in the reflection pixels
with respect to the reflection areas provided therein is larger
than the size ratio of the transparent areas provided in the
translucent pixels with respect to the reflection areas provided
therein. In such a way, the brightness is ensured by transmission
light though the transparent areas of the reflection pixels.
Moreover, in each of the red and green color filters, the size
ratio of the transparent areas provided in the reflection pixels
with respect to the reflection areas provided therein is smaller
than the size ratio of the transparent areas provided in the
translucent pixels with respect to the reflection areas provided
therein. In such a way, degrees of whiteness of both of the
reflection pixels and the translucent pixels are adjusted, thus
making it possible to improve differences in reflectance and color
tone between the reflection areas and the translucent display
areas.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing a schematic structure of a periphery
of an image area in a conventional liquid crystal display
device.
FIG. 2 is a plan view showing a schematic configuration of a
periphery of an image area in a liquid crystal display device of a
first embodiment.
FIG. 3 is a cross-sectional view showing a schematic structure of a
translucent pixel arrayed on the image area of FIG. 2.
FIG. 4 is a cross-sectional view showing a schematic structure of a
reflection pixel arrayed on a dummy area of FIG. 2.
FIG. 5 is an enlarged plan view showing the respective pixels in a
vicinity of a boundary between the image area and dummy area of
FIG. 2.
FIG. 6 is a cross-sectional view showing a schematic structure of a
translucent pixel arrayed on an image area of comparative
example.
FIG. 7 is a cross-sectional view showing a schematic structure of a
reflection pixel arrayed in a dummy area of comparative
example.
FIG. 8 is an enlarged plan view showing the respective pixels in a
vicinity of a boundary between an image area and a dummy area in a
liquid crystal display device of a second embodiment.
DESCRIPTION OF THE EMBODIMENT
First Embodiment
As shown in a plan view of FIG. 2, in a liquid crystal display
device of a first embodiment, a dummy area 2 that always displays
white color is provided on a peripheral area between an image area
1 and a frame-like black mask 3.
On the image area 1, a plurality of translucent pixels that have
reflection areas and transmission areas are arrayed. In the
transmission areas, an image is displayed by a light transmission
mode. Meanwhile, in the reflection area, an image is displayed by a
light reflection mode using the external light.
On the dummy area 2, a plurality of reflection pixels that have
only reflection areas are arrayed. In the reflection areas, the
white color is always displayed by a light reflection mode using
the external light. Note that, in this liquid crystal display
device, the white color is displayed on both of the image area 1
and the dummy area 2 when a voltage is not applied to a liquid
crystal layer (normally white display).
Next, a description will be made of a configuration of the
translucent pixel arrayed in the image area 1 by using a
cross-sectional view of FIG. 3. As shown in FIG. 3, this liquid
crystal display device includes a liquid crystal layer 103 between
an array substrate 101 and an opposite substrate 102, which are
arranged opposite to each other. A backlight 104 is disposed on a
back surface side of the array substrate 101.
In the array substrate 101, an insulating layer 106 is formed on an
upper surface of a glass substrate 105, and a transmission
electrode 109 is formed on the insulating layer 106. In the case of
a reflection area 6, a reflection electrode 110 is further formed
on the transmission electrode 109. The transmission electrode 109
and the reflection electrode 110 form a pixel electrode 108.
In the opposite substrate 102, a color filter 8, a black matrix
111, an overcoating layer 112, and an opposite electrode 113 are
formed on a lower surface of a glass substrate 105.
The translucent pixel includes the reflection area 6 having the
reflection electrode 110, and the transmission area 7 having only
the transmission electrode 109. In the reflection area 6, the image
is displayed by using the external light reflected on the
reflection electrode 110. Meanwhile, in the transmission area 7,
the image is displayed by using light from the backlight 104, which
has been transmitted through the transmission electrode 109. The
translucent pixel has a multi-gap structure having different cell
gaps between the reflection area 6 and the transmission area 7, in
which a cell gap L2 of the reflection area 6 is smaller than a cell
gap L1 of the transmission area 7.
Next, a description will be made of a configuration of the
reflection pixel arrayed in the dummy area 2 by using a
cross-sectional view of FIG. 4. As shown in FIG. 4, the reflection
pixel has a single-gap structure having only a reflection area 10
in which the reflection electrode 110 is formed. White color is
always displayed by reflecting the external light in the reflection
area 10. Note that other basic structures of the reflection pixel
are similar to those of the translucent pixel, and accordingly, the
same reference numerals are assigned to the same constituents as
those in FIG. 3, and a description thereof is omitted here.
However, in FIG. 4, reference numeral 11 denotes a transparent area
to be described later, and reference numeral 107 denotes a
thin-film transistor.
Next, a description will be made of the configurations of the
respective reflection areas in the reflection pixel and the
translucent pixel by using a plan view of FIG. 5. In FIG. 5, the
respective pixels in the vicinity of a boundary between the image
area 1 and dummy area 2 of FIG. 2 are shown enlargedly. A
translucent pixel 4 and a reflection pixel 6 are arranged in the
image area and the dummy area, respectively.
The translucent pixel 4 is composed of three pixels having RGB
color filters 8R.sub.1, 8G.sub.1 and 8B.sub.1. In the reflection
area 6, transparent areas 9R, 9G and 9B are provided in the color
filters 8R.sub.1, 8G.sub.1 and 8B.sub.1, respectively. Here, a size
of the reflection area 6 is represented as S' and a size of the
transparent areas 9 of the color filters is represented as
S'.sub.CF.
The reflection pixel 5 is composed of three pixels having RGB color
filters 8R.sub.2, 8G.sub.2 and 8B.sub.2. In the reflection area 10,
transparent areas 11R, 11G and 11B are provided in the color
filters 8R.sub.2, 8G.sub.2 and 8B.sub.2, respectively. Here, a size
of the reflection area 10 is represented as S, and a size of the
transparent areas 11 of the color filters is represented as
S.sub.CF.
In this liquid crystal display device, in the color filters 8 of at
least the same one color, a size ratio S.sub.CF/S obtained in such
a manner that the size of the transparent area 11 of the color
filter in the reflection pixel 5 is divided by the size of the
reflection area 10 therein is set so as to be larger than a size
ratio S'.sub.CF/S' obtained in such a manner that the size of the
transparent area 9 of the color filter in the translucent pixel 4
is divided by the size of the reflection area 6 therein.
Specifically, first, the size S of the reflection area 10 of the
reflection pixel 5 is equalized to the size S' of the reflection
area 6 of the translucent pixel 4. In such a way, the
above-described size ratios can be easily adjusted only by the size
S'.sub.CF of the transparent areas 9 and the size S.sub.CF of the
transparent areas 11 at a time of manufacturing the color filters
8.
Then, the size S.sub.CF of each transparent area 11 of the color
filters 8R.sub.2, 8G.sub.2 and 8B.sub.2 in the reflection pixel 5
is made larger than the size S'.sub.CF of each transparent area 9
of the color filters 8R.sub.1, 8G.sub.1 and 8B.sub.1 in the
translucent pixel 4. This relationship is represented below by
expressions. Blue color filter S'.sub.CF<S.sub.CF Red color
filter S'.sub.CF<S.sub.CF Green color filter :
S'.sub.CF<S.sub.CF
With such a configuration, brightness of the display is balanced by
adjusting quantities of transmission light through the transparent
areas 11 of the color filters of the reflection pixel 5 with
respect to quantities of the reflection light generated
unexpectedly on the transmission area 7 of the color filters of the
translucent pixel 4.
Next, a description will be made of a liquid crystal display device
of comparative example. In comparative example, as in FIG. 2, the
dummy area 2 is provided on the peripheral area between the image
area 1 and the frame-like black mask 3. On the image area 1, the
translucent pixels that have the reflection areas and the
transmission areas are arrayed. The image area 1 displays the color
image by the light reflection mode and the light transmission mode.
On the dummy area 2, the reflection pixels that have only the
reflection areas are arrayed. The dummy area 2 always displays the
white color by the light reflection mode.
A cross-sectional view of the translucent pixel in the image area 1
of comparative example is as shown in FIG. 6. The translucent pixel
in FIG. 6 is basically similar to that in FIG. 3, and however, has
a configuration without the transparent area 9 in the color filter
8. In addition, a cross-sectional view of the reflection pixel in
the dummy area of comparative example is as shown in FIG. 7. The
reflection pixel in FIG. 7 is basically similar to that in FIG. 4,
and however, has a configuration without the transmission area 11
in the color filter 8.
In comparative example, the translucent pixel of the image area and
the reflection pixel of the dummy area are different in structure
from each other, and accordingly, differences in reflectance ratio
and color tone occur therebetween. According to this, in the case
of the reflection display of the white color, the boundary between
the image area and the dummy area will become conspicuous.
As described above, according to this embodiment, in the color
filters 8 of at least the same one color, the size ratio of the
transparent area 11 to the reflection area 10 in the reflection
pixel 5 is larger than the size ratio of the transparent area 9 to
the reflection area 6 in the translucent pixel 5. In such a way,
the brightness of the display is balanced by adjusting the quantity
of the transmission light through the transparent area 11 of the
reflection pixel 5 with respect to the quantity of the reflection
light generated unexpectedly on the transmission area 7 of the
translucent pixel 4. Moreover, degrees of whiteness in the
translucent pixel 4 and the reflection pixel 5 are approximated to
each other. Accordingly, the differences in reflectance ratio and
color tone between the image area 1 and the dummy area 2 can be
eliminated, thus making it possible to make the boundary
therebetween inconspicuous.
Moreover, according to this embodiment, the size S of the
reflection area 10 of the reflection pixel 5 is equal to the size
S' of the reflection area 6 of the translucent pixel 4. In such a
way, it becomes possible to easily adjust the above-described size
ratio only by the size S' of each transparent area 9 of the color
filters and the size S.sub.CF of each transparent area 11 of the
color filters.
Second Embodiment
A configuration of a liquid crystal display device in a second
embodiment is basically similar to that described in the first
embodiment. Different points of the second embodiment from the
first embodiment are the following two. The first point is that the
size S of the reflection area 10 of the reflection pixel 5 is
larger than the size S' of the reflection area 6 of the translucent
pixel 4. The second point is that, in the blue color filters 8B,
the size ratio S.sub.CF/S obtained in such a manner that the size
of the transparent area in the reflection pixel 5 is divided by the
size of the reflection area therein is larger than the size ratio
S'.sub.CF/S' in the translucent pixel 4, and in each of the red and
green color filters 8R and 8G, the size ratio S.sub.CF/S obtained
in such a manner that the size of the transparent area in the
reflection pixel 5 is divided by the size of the reflection area
therein is smaller than the size ratio S'.sub.CF/S' in the
translucent pixel 4. A description will be mainly made of portions
of this embodiment, which are different from those of the first
embodiment, and a description of duplicate portions will be
omitted.
FIG. 8 is a plan view enlargedly showing a pixel in a vicinity of
an image area and a dummy area in the liquid crystal display device
of the second embodiment. The translucent pixel 4 and the
reflection pixel 5 are arranged in the image area and the dummy
area 2, respectively.
The size S of the reflection area 10 of the reflection pixel 5 is
larger than the size S' of the reflection area 6 of the translucent
pixel 4.
In the blue color filters 8B.sub.1 and 8B.sub.2, the size ratio
S.sub.CF/S obtained in such a manner that the size of the
transparent area 11 in the reflection pixel 5 is divided by the
area of the reflection area 10 therein is larger than the size
ratio S'.sub.CF/S' in the translucent pixel 4. Moreover, in each of
the red and green color filters 8R and 8G, the size ratio
S.sub.CF/S obtained in such a manner that the size of the
transparent area 11 in the reflection pixel 5 is divided by the
size of the reflection area 10 therein is smaller than the size
ratio S'.sub.CF/S' in the translucent pixel 4. This relationship is
represented below by expressions.
Blue color filter: S'.sub.CF/S'<S.sub.CF/S
Red color filter: S'.sub.CF/S'>S.sub.CF/S
Green color filter: S'.sub.CF/S'>S.sub.CF/S
With such a configuration, in the blue color filters 8B, the
brightness is ensured by the transmission light through the
transparent areas 11 of the reflection pixel 5. Moreover, in each
of the red and green color filters, the degrees of whiteness of
both of the reflection pixel 5 and the translucent pixel 4 are
adjusted.
As described above, according to the second embodiment, the size S
of the reflection area 10 in the reflection pixel 5 is larger than
the size S' of the reflection area 6 in the translucent pixel 4. In
the blue color filters 8B, the size ratio S.sub.CF/S of the
transparent area 11 in the reflection pixel 5 with respect to the
reflection area 10 therein is larger than the size ratio
S'.sub.CF/S' in the translucent pixel 4. Hence, the brightness can
be ensured by the transmission light through the transparent areas
11 of the reflection pixel 5.
Moreover, in each of the red and green color filters 8R and 8G, the
size ratio S.sub.CF/S of the transparent area 9 in the reflection
pixel 5 with respect to the reflection area 10 therein is smaller
than the size ratio S'.sub.CF/S' in the translucent pixel 4. In
such a way, the degrees of whiteness of both of the reflection
pixel 5 and the translucent pixel 4 are adjusted, thus making it
possible to improve the differences in reflectance ratio and color
tone between the image area 1 and the dummy area 2, and to make the
boundary between the image area 1 and the dummy area 2
inconspicuous in case of the reflection display of the white
color.
Other Embodiments
In the color filters 8R, 8G and 8B in the first embodiment, and
only in the color filters 8B in the second embodiment, the
configuration is adopted, in which the size ratio S.sub.CF/S in the
reflection pixel 5 is larger than the size ratio S'.sub.CF/S' in
the translucent pixel 4. However, the configuration of the present
invention is not limited to the above, and each size ratio in the
color filters 8 of at least the same one color just needs to
satisfy the above-described magnitude relationship. For example,
each size ratio in the color filters of two colors may satisfy the
above-described magnitude relationship, and the reflectance and the
degree of whiteness may be adjusted by the reflection pixel 5 and
the translucent pixel 4.
Moreover, with regard to the size S of the reflection area 10 of
the reflection pixel 5 and the size S' of the reflection area 6 of
the translucent pixel 4, both of the sizes are equal to each other
in the first embodiment, and the size S is larger than the size S'
in the second embodiment. However, the configuration of the present
invention is not limited to the above. For example, the size S of
the reflection area 10 of the reflection pixel 5 may be made
smaller than the size S' of the reflection area 6 of the
translucent pixel 4, and the above-described size ratio may be
adjusted so that the differences in reflectance ratio and color
tone between the image area 1 and the dummy area 2 can be
improved.
Moreover, in the above-described respective embodiments, the color
filters of three colors, which are red, blue, and green, are used.
However, the configuration of the present invention is not limited
to this. For example, not only the above-described three colors but
also other colors may be combined.
* * * * *